The negative environmental impact of fossil fuels and their rising cost have resulted in a need for cleaner, cheaper alternative energy sources. Among different forms of alternative energy sources, solar power has been favored for its cleanness and wide availability.
A solar cell converts light into electricity using the photovoltaic effect. Most solar cells include one or more p-n junctions, which can include heterojunctions or homojunctions. In a solar cell, light is absorbed near the p-n junction and generates carriers. The carriers diffuse into the p-n junction and are separated by the built-in electric field, thus producing an electrical current across the device and external circuitry. An important metric in determining a solar cell's quality is its energy-conversion efficiency, which is defined as the ratio between power converted (from absorbed light to electrical energy) and power collected when the solar cell is connected to an electrical circuit. High efficiency solar cells are essential in reducing the cost to produce solar energy.
One important factor affecting the energy-conversion efficiency of a solar cell is its internal resistance. Reducing resistive loss can increase the energy outputted by the solar cell, and hence the solar cell's efficiency. It has been shown that electrode grids based on electroplated Cu have significantly lower resistivity than conventional screen-printed Ag grids. In addition to having lower resistivity, electroplated Cu grids also cost less than the Ag grids. However, unlike Ag, Cu can be susceptible to oxidation and corrosion. When exposed to moisture, Cu grids may oxidize, resulting in increased resistivity and decreased strength. Therefore, Cu grids of solar cells are often coated with a corrosion-resistive protection layer. Conventional approaches for coating Cu grids with such a corrosion-resistive protection layer can generate hazardous waste.